Evidence from previous cross-sectional and prospective studies on the effect of levonorgestrel implant (Norplant) use on the cardiovascular risk factor profile of premenopausal women is indeterminate. To date no randomized clinical trial has been conducted directly comparing the effects of levonorgestrel implant use to oral contraceptive use on the cardiovascular risk profile of premenopausal women. We hypothesize that levonorgestrel implant use when compared with use of a low dose oral contraceptive (Triphasil), which contains both ethinyl estradiol and levonorgestrel, may have an adverse effect on lipid metabolism, resulting in a decrease in total high density lipoprotein (especially the HDL-2 subfraction), a decrease in apolipoprotein A1, an increase in low density lipoprotein, and an increase in apolipoprotein B. We also hypothesize that levonorgestrel implant use when compared with use of a low dose oral contraceptive (Triphasil) may: (1) have an adverse effect on blood pressure resulting in an increased risk of hypertension; (2) have an adverse effect on glucose metabolism resulting in hyperglycemia and hyperinsulinemia; and (3) have an adverse effect on the coagulation system resulting an increased risk of a hypercoagulable state, with subsequent increased risk of both thromboembolic and atherosclerotic disease. This proposed randomized clinical trail provide a rigorous test of whether levonorgestrel implant use compared to use of a state of the are oral contraceptive increases cardiovascular risk factors in premenopausal women.